ABSTRACT: As outlined in DAT18-08, NIDA has a strong interest in understanding treatment utilization among persons with opioid use disorders (POUDs) as they transition from prison to the community, because treating individuals with opioid use disorder (OUD) simultaneously improves public health and public safety. Kentucky is in the midst of an opioid crisis, with many POUDs cycling through the criminal justice system each year. While evidenced-based medications for addiction treatment (MAT) exist for treating OUD, MAT is underutilized within prisons, which elevates the risk of relapse and overdose when POUDs are released and re-enter their communities. Research is scant regarding the multi-level factors associated with offenders? willingness to initiate MAT while in prison and their continued engagement in treatment after release. Furthermore, rural and urban populations have not been compared. In response to NIDA DAT18-08, we propose to conduct the high-impact Geographic variation in Addiction Treatment (GATE) study, which will address the knowledge gap on multi-level factors influencing prison-based extended-release injectable naltrexone (XR-NTX) initiation as well as examine predictors of post-release MAT use and adverse outcomes (i.e., relapse, overdose, recidivism) among both rural and urban POUDs. This mixed methods study employs a social ecological framework to understand individual characteristics that influence MAT initiation and adverse outcomes, as well as contexts more distal to the individual, including social networks and structural factors. The specific aims of the GATE study are: 1) to identify the individual, personal network, and structural factors associated with XR-NTX initiation in prison among rural, as compared to urban, POUDs, and 2) to examine the individual, personal network, and structural factors predicting MAT use, treatment use, and adverse outcomes in the community among re-entering rural, as compared to urban, POUDs over time. A prospective observational longitudinal cohort study will be conducted with 500 POUDs, using survey and social network data collected in prison and at 6- and 12-months post-release to explore multi-level rural-urban variation in key outcomes. In-depth guided qualitative interviews will be conducted with POUDs, prison-based treatment staff, and social service clinicians. To maximize rigor and reproducibility, we will employ a concurrent triangulation strategy, whereby qualitative and quantitative data contribute equally to the analysis and are used for cross-validation. This study is led by a qualified interdisciplinary team and is the first mixed methods study examining the processes of social influences that occur in rural and urban social networks as POUDs transition from prison back to geographically diverse counties. The GATE study will enhance our ability to address the opioid epidemic within the correctional contexts of prisons and community supervision by informing process improvement efforts for prison-based MAT initiation and post-release retention in care, applying network science findings to improve the re-entry planning process, and establishing the foundation for future R-level intervention applications.